1. Field of the Invention
The present invention relates to a position sensor which detects the range of a transmission selected by the shift lever of a vehicle.
2. Description of the Related Art
A transmission mounted on a vehicle generally has a neutral range in which an input driving force is not transmitted to the output side of the transmission, a reverse range for causing the vehicle to move backward, a drive range for causing the vehicle to move forward, and other ranges. A driver of the vehicle selects the ranges as appropriate in accordance with the driving situations.
Some of such transmissions include a plurality of hydraulically actuated mechanisms such as a clutch, a brake, and so on. These hydraulically actuated mechanisms are configured to be switchable between a transmission state where the driving force is transmitted and an open state where the transmission state is released, according to whether oil pressure is supplied or not.
In this transmission, the states of the respective hydraulically actuated mechanisms are set for each of the ranges of the transmission. More specifically, when a certain range of the transmission is selected by the shift lever mounted on the vehicle, the states of the hydraulically actuated mechanisms are switched to the predetermined states such that the range of the transmission is switched to the selected range.
Conventionally, as means for switching the states of the hydraulically actuated mechanisms in accordance with the selected range of the transmission, a manual valve has been used. This manual valve has output ports corresponding respectively to the ranges of the transmission. The manual valve is mechanically connected to the shift lever via wire and the like, so that the manual valve moves in correspondence with the manipulation of the shift lever. At this time, the manual valve outputs oil pressure from the output port corresponding to the range that has been selected by the driver with the shift lever.
Such a manual valve is required to have a plurality of lands corresponding to the number of ranges in the shift lever. As the number of ranges increases, the manual valve needs to be increased in length, hindering downsizing thereof.
In recent years, with an increasing demand for downsized vehicles, it has been considered to switch the ranges of the transmission without the use of the manual valve which is difficult to downsize. As a vehicle using no manual valve, there is known a vehicle, as disclosed in Japanese Patent No. 2666645, which includes four solenoid valves that switch whether to supply oil pressure or not. These solenoid valves have their on and off states switched in accordance with the range selected by the shift lever. In this vehicle using no manual valve working in correspondence with the shift lever, an ECU detects the state of a switch that works in correspondence with the shift lever, and switches the on and off states of the respective solenoid valves.
In the case of using a conventional manual valve, which works in correspondence with the shift lever, when a range is selected by the shift lever, oil pressure is supplied to the hydraulically actuated mechanism(s) corresponding to the selected range without fail. In the case of detecting a range on the basis of the state of an electrical switch, however, when a short circuit or break occurs in the contacts of the switch, the ECU may not be able to detect the range selected by the shift lever. In order to prevent such an undesirable situation, it should be necessary to detect abnormalities in the contacts.